What Is Glucose in a Blood Test?

Glucose is your body's primary energy source, regulated by insulin (lowers) and glucagon (raises).

Fasting Reference Ranges

• Normal: 70–99 mg/dL
• Prediabetes: 100–125 mg/dL
• Diabetes: 126 mg/dL+ (two separate tests)
• Hypoglycemia: below 70 mg/dL
• Random diabetes threshold: 200 mg/dL+ with symptoms

High Glucose Causes

• Diabetes (Type 1 or 2)
• Prediabetes
• Stress — illness, surgery
• Corticosteroids
• Pancreatic disease
• Pregnancy — gestational diabetes

Low Glucose Causes

• Diabetes medication — insulin or sulfonylureas
• Excessive alcohol
• Insulinoma — rare tumor
• Severe liver disease
• Adrenal insufficiency

Glucose vs HbA1c

• Fasting glucose = snapshot
• HbA1c = 3-month average
• HbA1c 5.7–6.4% = prediabetes
• HbA1c 6.5%+ = diabetes
• HbA1c is more reliable for diagnosis